The present invention refers to new heparin derivatives having antithrombotic activity, also endowed with reduced hemorrhagic and anticoagulant activity, obtained by treating in a basic medium heparins of various origin, optionally in the presence of alkali metal salts and of a reducing agent.
It is known that heparin-like structures can be modified in various manners by treating them in a basic medium.
In European Publication EP No. 0133078, Mardiguian J. S., depolymerizes the heparin into oligosaccharides fractions containing from 4 to 20 saccharides units, by treating the benzyl ester of the heparin by means of an organic or inorganic base, at a concentration between 0.1 and 0.6 molar at a temperature between 20.degree. C. and 80.degree. C. Such depolymerization is accompanied by the formation of a double bond in the positions 4 and 5 of the uronic acid, detectable by U.V. absorption at 230 nm.
Hirano S. et al., Conn. Tissue Res., 3, 73-79, 1975 depolymerize the heparin and other glycosaminoglycans in strong basic medium, by using from 2 to 10 molar concentrations of sodium or barium hydroxide at temperatures higher than 80.degree. C. In this way they get a strong depolymerization following the cleavage of the glucosidic bond between the position 1 of glucosamine units and the position 4 of adjacent uronic units. Moreover such depolymerization is accompanied by the formation of a double bond in the positions 4 and 5 of the uronic acid, detectable by means of an absorption at 225-230 nm in the U.V. spectrum.
Sampson P. and Meyer K., Proc. Nat. Acad. Sci. U.S.A., 68, 2329-2331, 1971, obtained a structural modification in the glucosamine unit with formation of 3,6-anhydroglucosamine by treating heparin with 1N sodium hydroxide in the presence of sodium borohydride at 80.degree. C. for 7 hours.
The heparin derivatives object of the present invention totally differ from those described in the prior art. In fact they do not show the chimico-physical properties of the compounds obtained by Mardiguian J. S. and by Hirano S. et al., as it is shown by the average molecular weight which remains substantially unchanged, thus proving the lack of depolymerization, and by the lack of absorption at 225-230 nm in U.V. and of peaks corresponding to the resonances of the double bond in the .sup.13 C-NMR, which demonstrate the lack of the double bond in the positions 4 and 5 of the uronic acid. Moreover they do not even show the chimico-physical properties of the compounds isolated by Sampson P. and Meyer K. as the .sup.13 C-NMR spectrum of the compounds obtained in the present invention shows unchanged the position and the intensity of the signal of the carbon atom in position 6 of the glucosamine and shows unchanged the intensity ratio between the 6-sulfated carbon atom and the 6-desulfated carbon atom that should change in case of formation of 3,6-anhydroglucosamine because of the participation of the 6-sulfated carbon atom in the formation of the anhydroderivative.